Electric circuit breakers

ABSTRACT

In an electric circuit breaker having a pivotable armature which is caused to swing, upon passage of a short circuit current, to actuate a trip bar to trip the circuit breaker, the load against which the armature is swung is variable by adjustment of an eccentric boss accessible outside the circuit breaker.

United States Patent [191 Kidd et al.

[451 Sept. 16, 1975 ELECTRIC CIRCUIT BREAKERS lnventors: Alan Lister Kidd, Southport;

Douglas Eaves, Blackpool; Keith Walmsley, Preston, all of England Dorman Smith Switchgear Limited, Preston, England Filed: Sept. 12, 1974 App]. No.: 505,224

Assignee:

Foreign Application Priority Data Oct. 4, 1973 United Kingdom 46292/73 us. Cl 335/42'; 335/176 lnt. cl. HOIH 69/01 Field of Search 335/176, 42, 8,9, 10,

[56] References Cited UNITED STATES PATENTS 3,084,236 4/1963 Klein et a1. 335/10 3,142,187 7/1964 Kane et a1 74/553 3,391,361 7/1968 Jencks et a1. 335/176 3,775,713 11/1973 Walker et a1. 335/176 Primary Examiner-Harold Broome Attorney, Agent, or Firm-Ross, Ross & Flavin ABSTRACT In an electric circuit breaker having a pivotable armature which is caused to swing, upon passage of a short circuit current, to actuate a trip bar to trip the circuit breaker, the load against which the armature is swung is variable by adjustment of an eccentric boss accessible outside the circuit breaker.

4 Claims, 12 Drawing Figures PATENTED SEP BIQTS 39 QOBA 1 SHEET 2 2 ELECTRIC CIRCUIT BREAKERS This invention concerns electric circuit breakers of the type which includes a pivoted armature forming part of an electromagnetic circuit through which a conductor extends so that a short circuit current passing through the conductor causes pivoting of the armature by reason of magnetism induced in the electromagnetic circuit by such current, the armatures movement serving to cause movement of a trip bar of the circuit breaker, whereby the latter is tripped.

An object of the invention is to provide a simple arrangement permitting adjustment of the force against which the armature must pivot to cause tripping of the breaker, whereby the rating of the circuit breaker can be varied and the breaker can be set manually to a selected rating in a current range.

With this object in view the present invention provides an electric circuit breaker of the kind referred to wherein pivoting movement of the pivoted armature occurs against the action of a resilient member loading the armature, and is characterised in that the load applied by said resilient member is variable by adjustment of an eccentric boss rotatable manually by means of a knob accessible externally of the circuit breaker.

Conveniently the knob is shaped to provide a recess in which the boss is secured, and the securement of the boss to the knob is preferably adjustable to provide for the eccentricity of the boss to be varied thereby to vary the extent of adjustment which is achieved by rotating the knob.

The boss and the knob are conveniently formed the one with a groove and the other with a complementary rib engaging with the groove, said rib and groove extending diametrically relative to the axis of rotation of the knob and providing for corresponding diametral adjustment of the boss.

In a preferred practical embodiment of the invention a pivoted lever, having the resilient member connected thereto, abuts the eccentric boss and is adapted to be adjusted in its pivotal position by rotation of the boss, thereby to vary the loading applied to the armature by the resilient member.

The resilient member is conveniently a spring connected by one end to the lever and by the other end to the pivoted armature.

In order that the invention may be fully understood, it will be described further, by way of example, with reference to the accompanying drawings, in which:-

FIG. 1 is an elevation of the tripping mechanism of a three-pole circuit breaker conforming to the present invention;

FIG. 2 is a plan view taken as indicated by the arrow II of FIG. I; I

FIG. 3 is a cross-section through any of the three poles of the circuit breaker as indicated by the three section lines III-III in FIG. 1 certain of the components of the mechanism being omitted or broken away for clarity;

FIG. 4 is a detached elevation showing a boss and knob which form part of the mechanism of FIGS. 1 to 3 these being shown in one end position of adjustment;

FIG. 5 is a view similar to FIG. 4 but showing the boss and knob in a median position;

FIG. 6 is a view similar to FIGS. 4 and 5 but showing the boss and knob in its other end position of adjustment;

FIG. 7 is an elevation showing the knob alone;

FIG. 8 is a plan view corresponding to FIG. 7;

FIG. 9 is a side view corresponding to FIGS. 7 and 8;

FIG. 10 is a rear elevation of the boss alone;

FIG. 11 is a sectional plan corresponding to FIG. 10; and

FIG. 12 is a front elevation of the boss.

The illustrated tripping mechanism of an electric circuit breaker conforming to the invention comprises a trip bar 10 which is common to and extends across the three poles of the-circuit breaker, which poles are indicated generally at A, B and C. This trip bar 10 is mounted so as to be pivotable, about an axis which extends longitudinally of the trip bar 10, from the position shown in FIG. 3 in a clockwise direction, to effect tripping of the circuit breaker.

An electromagnetic circuit for each pole of the circuit breaker comprises a substantially U-shaped electromagnetic element 11 to one limb 12 of which a respective armature 13 is pivotally connected by a pivot 14, the armature 13 being connected by one end to the limb 12, and projecting by its other end over the other limb 15. The element 11 and armature 13, as well as their associated components, have been omitted from poles A and C in FIG. 1 and have been shown only at pole B, so as to facilitate appreciation of all of the components of the mechanism.

A pull rod 16 is pivotally connected by its lower end to the armature 13 approximately midway along the length of the latter and extends through a gap provided between a pair of tongues 17 formed integrally with and projecting from the trip bar 10, being provided with an adjustable nut 18 at the end remote from the armature 13. It will thus be understood that upon the armature l3 pivoting from its position shown in FIG. 1, in a clockwise direction, the resultant movement of the pull rod 16 causes the nut 18 to engage with the tongues 17 and effect pivoting of the trip bar 10 to trip the breaker. In operation of the circuit breaker, such pivoting of the armature 13 will occur in the event of passage of a short circuit current passing through a conductor 50 extending through the electromagnetic circuit provided by the electromagnetic element 11 and the armature 13, by reason of magnetism induced in such circuit by the short circuit' current.

The armature 13 is resiliently loaded into its rest position, which is illustrated in FIG. 1 and which is defined by a stop screw 19 through an angle piece 20 of a stop strip 21 (see FIG. 3) bolted to the limb 15 of the electromagnetic element 11, by a resilient member in the form of a helical tension spring which is indicated generally by the reference numeral 22. One end of the spring 22 is connected to the free end of the armature l3 and the other end thereof is connected to an adjusting bolt 23 through a respective angle piece 24 provided integrally with a lever 25 which is pivoted at 26.

The load applied by the spring 22 to the pivoted armature 13 is variable by adjustment of an eccentric boss 27 against which abuts a lug 28 formed integrally with the lever 25, the pivotal position of the lever 25 about its pivot 26 depending upon the eccentric location of the boss 27. The spring 22 acts on the lever 25, of course, in such a way as to ensure that the lug 28 is always in contact with the boss 27.

From FIGS. l0, l1 and 12 it will be seen that the boss 27 comprises a body 29 having a slot 30 there-through, ribs 31, 32 being provided at each end of the body 29 and in alignment with the longitudinal centre line of the slot 30. To one side of the slot 30 is a counterbored fixing hole 33.

As can be seen from FIGS. 3 to 6, the boss 27 is secured to a knob 34 which, as will be evident from FIGS. 2 and 3, is accessible from outside the circuit breaker so as to be manually rotatable about an axis provided by a pivot bolt 35. The configuration of the knob 34 is shown in FlGS. 7, 8 and 9. It comprises an approximately semi-circular back plate 36 having a flange portion 37 extending therearound so as to define a recess, and formed with a bush 38 by which it fits over the bolt 35. Two shallow grooves 39, 40 are provided at opposite sides of the bush 38 a as to be substantially diametrically disposed relative thereto and spaced to one side of these grooves 39, 40 and the bush 38, so as to be substantially parallel to the grooves 39, 40 is a fixing slot 41. The boss 27 is located on the knob 34 by its ribs 31, 32 engaging into the respective grooves 40, 39 and is fixed in position by a screw 42 through the fixing slot 41 and the counterbored fixing hole 33. FIGS. 4 to 6 show the boss 27 fixed in its position of maximum eccentricity so that rotation of the knob 34 provides max imum variation of the loading applied to the pivoted armature 13 by the spring 22. Thus, for example, a circuit breaker may be adjusted to trip at selected currents in the range of 3000 amperes to 10,000 amperes.

The extent of adjustment achieved by rotating the knob 34, however, is variable by varying the eccentricity of the boss 27 and this is achieved by slackening off the screw 42 and displacing the boss 27 appropriately in the direction dictated by the interengagement of the ribs 31, 32 into the grooves 40, 39, it being possible to bring the boss 27 to a position wherein the centre of its body 29 nearly coincides with the axis of rotation of the knob 34 and only minimal or very fine adjustment is achieved by rotation of the knob 34.

It will be appreciated that adjustment of the boss eccentricity when the combination is in the maximum set positionas shown in FIG. 4 does not affect the tension of the spring 22 and the tripping performance of the breaker pole can be set at its upper limit when the combination is in this FIG. 4 position by adjustment of the bolt 23 only. This is because the direction of movement of the boss 27 to alter its eccentricity is substantially parallel to the lug 28 of the lever 25. When this has been done, the combination can be set to its minimum position and the tripping performance correspondingly set by adjustment of the eccentricity of the boss 27 alone. This latter adjustment will have no effect on the upper setting, which is substantially independent of the degree of eccentricity of the boss 27.

The described arrangement conforming to the inven tion accordingly provides, in a very simple and convenient manner, for the instantaneous tripping current of the circuit breaker to be adjusted and also for the available range of such adjustment to be varied.

in the illustrated case, a thermal element in the form of a respective bimetal strip 43 is provided for each of the poles A, B and C. This bimetal strip is arranged so as to be heated by current passingthrough the respective pole of the circuit breaker and, upon overload (i.e. passage of a sustained current in excess of a predetermined overload current rating of the breaker for a continuous period of time) to deflect sufficiently to engage a respective contact point, provided by a respective calibration screw 44, on the trip bar 10 to pivot the latter and cause tripping of the circuit breaker. It is not essential to the invention, however, that such thermal elements should be present.

We claim:

1. An electric circuit breaker of the type which includes a pivoted armature forming part of an electromagnetic circuit through which a conductor extends so that a short circuit current passing through the conductor causes pivoting of the armature by reason of magnetism induced in the electromagnetic circuit by such current, the armatures movement serving to cause movement of a trip bar of the circuit breaker, whereby the latter is tripped, and in which pivoting movement of the pivoted armature occurs against the action of a resilient member loading the armature, characterized in that the load applied by said resilient member is variable by adjustment of an eccentric boss rotatable manually by means of a knob accessible externally of the circuit breaker, the knob being shaped to provide a recess in which the boss is secured, and wherein the securement of the boss to the knob is adjustable for the eccentricity of the boss to be varied thereby to vary the extent of adjustment which is achieved by rotating the knob.

2. An electric circuit breaker as claimed in claim 1, wherein the boss and knob are formed the one with a groove and the other with a complementary rib engaging with the groove, said rib and groove extending diametrically relative to the axis of rotation of the knob and providing for corresponding diametral adjustment of the boss.

3. An electric circuit breaker as claimed in claim 2, wherein a pivoted lever, having the resilient member connected thereto, abuts the eccentric boss and is adapted to be adjusted in its pivotal position by rotation of the boss, thereby to vary the loading applied to the armature by the resilient member.

4. An electric circuit breaker as claimed in claim 3, wherein the resilient member is a spring connected by one end to the lever and by the other end to the pivoted armature. 

1. An electric circuit breaker of the type which includes a pivoted armature forming part of an electromagnetic circuit through which a conductor extends so that a short circuit current passing through the conductor causes pivoting of the armature by reason of magnetism induced in the electromagnetic circuit by such current, the armature''s movement serving to cause movement of a trip bar of the circuit breaker, whereby the latter is tripped, and in which pivoting movement of the pivoted armature occurs against the action of a resilient member loading the armature, Characterized in that the load applied by said resilient member is variable by adjustment of an eccentric boss rotatable manually by means of a knob accessible externally of the circuit breaker, the knob being shaped to provide a recess in which the boss is secured, and wherein the securement of the boss to the knob is adjustable for the eccentricity of the boss to be varied thereby to vary the extent of adjustment which is achieved by rotating the knob.
 2. An electric circuit breaker as claimed in claim 1, wherein the boss and knob are formed the one with a groove and the other with a complementary rib engaging with the groove, said rib and groove extending diametrically relative to the axis of rotation of the knob and providing for corresponding diametral adjustment of the boss.
 3. An electric circuit breaker as claimed in claim 2, wherein a pivoted lever, having the resilient member connected thereto, abuts the eccentric boss and is adapted to be adjusted in its pivotal position by rotation of the boss, thereby to vary the loading applied to the armature by the resilient member.
 4. An electric circuit breaker as claimed in claim 3, wherein the resilient member is a spring connected by one end to the lever and by the other end to the pivoted armature. 